The assembling of two video streams in the compressed domain is currently investigated but no implementation has been proposed yet. Even if both streams have been coded with the same parameters, they cannot be just concatenated in the case of the MPEG4 standard. Indeed, a MPEG4 video stream comprises Video Object Planes VOPs, each VOP being associated with a time stamp. These time stamps are necessary to insure the continuity of the time line. In MPEG4 video streams, said time stamps are coded using variable length codes. It is therefore not possible to just change some bits in each VOP headers in order to insure the time line continuity.
An obvious approach would be to decode each VOP of the second of the two video streams to be assembled and to re-code it with a modified time stamp taking into account the last time stamp of the first of the two video streams.
However, this solution is not satisfactory since, on the one hand, it degrades the visual quality of the second video stream and, on the other hand, it is resource consuming.